Environ. Sci. Technol. 2003, 37, 840-844
Indication of Geographic Variations of Organochlorine Concentrations in the Blubber of Antarctic Weddell Seals (Leptonychotes Weddelli) W A L T E R V E T T E R , * ,†,‡ MARION WEICHBRODT,‡ AND ELKE STOLL‡ Institute of Food Chemistry, University of Hohenheim, Garbenstrasse 28, D-70599 Stuttgart, Germany, and Department of Food Chemistry, Friedrich Schiller University Jena, Dornburger Strasse 25, D-07743 Jena, Germany
A sample cleanup procedure using microwave-assisted extraction (MAE) with focus open vessel (FOV-MAE) technique was validated for the determination of organohalogen compounds in the blubber of a Weddell seal (Leptonychotes Weddelli) from the Antarctic (King George Island, 62° 14′ S, 58° 40′ W). Good reproducibility in replicate analysis of samples confirms the suitability of the method for samples with very low persistent organic pollutant (POP) concentrations. The method was used to analyze three additional blubber samples of Weddell seals from King George Island. This community of Weddell seals showed the lowest DDT (11-19 µg/kg) and PCB (12.5 µg/kg) concentrations so far detected in comparable marine mammals from all over the world. The concentrations determined in the four Weddell seals were also typical for the population at King George Island. However, the DDT and PCB concentrations on King George Island were one order of magnitude lower than in samples of the same species from other sites in the Antarctic (located between 69° S and 78° S). This suggests a wide variability of organohalogen levels in the Antarctic, depending on the geographic site. King George Island (62° S) is found at the outskirts of the Antarctic Peninsula, i.e., the region with the mildest climate in the Antarctic. Low organohalogen levels at this site were attributed to a lower degree of condensation in comparison with locations further south. Most of the reference samples were taken in the Weddell and Ross Seas, i.e., from coastlines as close as possible to the pole. Consequently, other sites on the same latitude as the Weddell and Ross Seas are found on the Antarctic continent. This raises the question whether high proportions of organohalogens are being deposited on the Antarctic continent where they are not available to marine organisms. Although this hypothesis has to be proven in follow-up studies, our study clearly demonstrates that it is complicated, if not impossible, to derive time trends in concentrations of POPs in biota from different reference sites in the Antarctic.
* Corresponding author phone: 49 711 459 4016; e-mail: w-vetter@ uni-hohenheim.de. † University of Hohenheim. ‡ Friedrich Schiller University Jena. 840
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Introduction Persistent organic pollutants (POPs) are found everywhere in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to both human and animal health (1). By 1966, POPs were already detected in Antarctic wildlife (2, 3). The bulk of POPs are transported via atmospheric long-range transport to polar regions where they condense due to the reduced vapor pressure at low temperatures. The mechanism of atmospheric transport of POPs toward polar regions has been described with several models (4-6). A key factor appears to be the temperature gradient between moderate and polar regions which finally leads to deposition of POPs in colder regions. For the protection of the global environment, as well as for a better understanding and prediction of the environmental fate and distribution of POPs, comprehensive research and global monitoring programs are being carried out. Most of the studies and research programs (e.g., the Arctic Monitoring and Assessment Program, AMAP) concentrate on the Arctic, including systematic measurements of POP concentration trends, food chain accumulation, and regional distribution. By contrast, systematic data on pollution in the Antarctic is hardly available despite recent efforts (7). While numerous studies have been carried out during the last 35 years, there is still no model that links data together to get a clearer picture of future trends (e.g., no reliable food web study has been carried out). In a preliminary study, we found significant differences in POP concentrations in marine wildlife from two different Antarctic sites. The goal of the present study was a quantitative evaluation with particular focus on the less polluted ecosystem, i.e., King George Island (62° 14′ S, 58° 40′ W). An initial screening of samples suggested that POP concentrations at King George Island are very low. For this reason we first validated a method using focus open vessel microwaveassisted extraction (FOV-MAE) followed by gel-permeation chromatography, and cleanup with deactivated silica (8, 9). This sample cleanup scheme has been previously applied to the determination of organohalogen compounds in seal blubber from polluted regions. This method was validated for the analysis of samples with very low organohalogen levels, i.e., samples from King George Island in the Antarctic. Sufficient material was available for the analysis of replicates. After determining the homogeneity of the samples, the results were compared with concentrations in the same species but from other sites in the Antarctic.
Materials and Methods Samples. Method validation was carried out with blubber of an adult Weddell seal (Leptonychotes Weddelli) found dead in January 1994 within walking distance from Base Cientifica Argentina Jubany, located at Maxwell Bay on King George Island (62° 14′ S, 58° 40′ W) (Figure 1). Weddell seals belong to the southern seals (Lobodontinae) and are distributed throughout the entire Antarctic continent. The total population is estimated at 750,000 individuals (10). Weddell seals are the most southerly year-round residents of the Antarctic. They inhabit the fast ice and show a distinct preference for lying on snow or ice, even when rock or shingle beaches are available. This species may reach up to 3 m length with a maximum weight of 500 kg. Weddell seals are sedentary and prefer to consume fish (>50% of all food items, e.g. Antarctic cod), although they feed on some squid and invertebrates at depths of about 400 m (10, 11). We evaluated additional samples from the same region as well. All individual samples 10.1021/es025949v CCC: $25.00
2003 American Chemical Society Published on Web 01/29/2003
FIGURE 1. Schematic map of Antarctica with dotted lines for 62° and 70° latitudes. Sampling points marked are KGI, King George Island (Jubany); DRE, Drescher Inlet; SYO, Syowa; McM, McMurdo; NEU, Neumayer (Atka Bay); AS, Amundsen-Scott Station (geographic South Pole); TNB, Terra Nova Bay; and GOU, Gould Bay. were from adults but the sex and exact age were not determined. We also applied the method on blubber of Weddell seals collected in 1985 and in January and February 1990 at the Drescher Inlet (72° 52′ S, 19° 25′ W), Vestkapp, Riiser Larsen Ice Shelf on the east coast of the Weddell Sea. Chemicals. Certified POP reference standards came from LGC Promochem, Wesel, Germany (PCB Mix I, N0813; pesticide mix, NC 378). Additional quantitative standard solutions came from LGC Promochem and Dr. Ehrenstorfer, Augsburg, Germany. The internal standard perdeuterated R-HCH (R-PDHCH) was synthesized in our lab (12). The standards have been used and evaluated for the quantification of POPs in certified cod liver oil 1588 (13). Instrumental. FOV-MAE was performed with a Soxwave 100 (Prolabo, Paris, France) system as recently described in detail (13, 14). However, handmade boron-silicate glass tubes (3.5 cm i. d., and length 29 cm) were used instead of quartz tubes. These showed the same performance as the quartz tubes during extraction, but are prone to damage due to excessive heating when very drastic extraction programs and samples with very high water content are used (data not shown). With the present program, however, (30 min at 75 W), no problems occurred. Automated gel-permeation chromatography (GPC) was carried out with a 33 cm × 2.5 cm i.d. glass tube filled with 50 g of bio beads S-X3 implemented in an Autoprep 1002 system (ABC, Analytical Biochemistry Columbia, USA) (8, 13). GC/ECD analyses were performed with a Hewlett-Packard 5890 series II gas chromatograph. A Y-piece installed at the exit of the split/splitless injector (splitless time 1.5 min) divided samples equally onto two capillary columns. The samples were injected automatically (HP 7673 autosampler). The capillary columns CP-Sil 2 and CP-Sil 8/20% C18 (both: length 50 m, 0.25 mm i. d., and 0.25 µm film thickness) were from Varian/Chrompack (Middelburg, The Netherlands). CP-Sil 2 is a very nonpolar stationary phase similar to squalane (and less polar than 100% dimethylpolysiloxane, e.g. DB-1) and the CP-Sil 8/20% C18 phase is similar to DB-5. Helium (quality 4.6; Linde, Leuna, Germany) was used as carrier gas at a constant flow rate of 1.3 mL/min. Nitrogen (quality 5.0, Linde) was used as makeup gas. The injector (splitless mode, split opened after 1.5 min) and detector temperatures were 250 °C and 300 °C, respectively. After injection at 60 °C (1.5 min) the GC oven temperature was ramped at 40 °C/min to 150 °C (5 min), then at 2 °C/min to 230 °C, and finally at 5 °C/min to 270 °C (15 min). The total run time was 71.75 min. Sample Cleanup. Approximately 2.5 g of seal blubber was accurately weighed into the extraction tubes, and an aliquot
of the internal standard R-PDHCH and 50 mL of ethyl acetate/ cyclohexane (1:1, v/v) were added. Extraction was performed with the program mentioned above. The content of the extraction flasks was filtered through Na2SO4 into 100-mL conical flasks. The extraction flasks and filters were washed with the extraction solvent and the liquid was transferred into the conical flasks. The volume was then adjusted to 10.0 mL in a rotavapor (RE 111, Bu¨chi, Flawil, Switzerland) connected with a CVC 2 vaccuum controller (vaccubrand, Wertheim, Germany) operated at 200 mbar (water bath temperature 30 °C). Ethyl acetate/cyclohexane evaporates in the azeotropic mixture of 54:46 volume % (boiling point 72.8 °C (15)), so that no significant change in the solvent occurred during this step. An 8-mL portion of this extract was passed through a 0.45-µm membrane filter and then into the GPC glass tubes (the remainder was used for gravimetric lipid determination; 73-79% lipids). GPC was performed with ethyl acetate/cyclohexane (1:1, v/v) at a flow rate of 4.6 mL/min (14, 16). A 5-mL portion of the 8 mL aliquot was used to fill the sample loop installed in the Autoprep system and the remaining 3 mL was discarded (only 50% of the sample was transferred to the GPC). The GPC eluate was concentrated in a rotavapor to 1-2 mL, and 2 mL of isooctane was added. In a nitrogen flow, the solvent was evaporated until ∼1 mL remained. This procedure was repeated twice for quantitative removal of ethyl acetate. A total of 3 g of deactivated silica (after drying silica for >16 h at 130 °C, 30% of water, w/w, was added (17)) was slurrypacked into a glass column (1.0 cm i.d.) and covered with Na2SO4. The isooctane extract of the sample was placed on the silica gel column and eluted with 60 mL of n-hexane (18). The volume of the eluate was reduced by rotary evaporation and by a gentle stream of nitrogen to 0.5 mL in calibrated flasks. A 0.1-mLportion of the sample was used for GC/ECD quantification of PCBs and organochlorine pesticides (“silica fraction”); and 0.4 mL of the sample was subjected to a PCB/ compounds of technical toxaphene (CTT) group separation. This aliquot was fractionated on a 30 cm × 1 cm i.d. glass column filled with 8 g of activated silica gel (>16 h at 130 °C) (19). PCBs were eluted with 48 mL of n-hexane (fraction 1), and CTTs and chlordane were eluted with 50 mL of n-hexane/ ethyl acetate (90:10, v:v) (fraction 2) (20). The fractions were concentrated (0.4 mL each) and analyzed by GC/ECD. Quantification of toxaphene, chlordane, and HCHs was carried out in fraction 2; PCBs, Q1, and DDT-related compounds were quantified in the silica fraction; PCBs were also quantified in fraction 1. Validation of the Sample Cleanup Methods. Quality control and method validation were based on recommendations of the European Commission (21). Several organochlorine compounds were determined by repetitive (n ) 5) cleaning and analysis of aliquots of blubber from one sample (see above). The recovery of the internal standard R-PDHCH (n ) 5) was 78(5%. A recent study has shown that loss of components is likely to occur for volatile organochlorines (R-HCH, lindane, HCB) during sample concentration steps. This study also revealed that loss of R-HCH was identical to the loss of the internal standard R-PDHCH (22). Using our laboratory method, we found no loss of penta- to heptachlorobiphenyl congeners (recovery rates 99.5-100.7%) but slight losses of HCB (89.9%), lindane (87.7%), and R-HCH (84.8%). From these results, we conclude that loss of PCBs, DDT and its metabolites, and toxaphene was low. Depending on the noise of the baseline and the ECD response of individual organohalogen compounds, the detection limits of the method ranged from 0.1 to 0.5 µg/kg. Based on sample weights of 1 g and a final volume of 0.5 mL, a concentration of 0.4 µg/kg (0.4 ng/g or 0.4 ng/mL; only 5 mL of the initial 10 mL were used to fill the sample loop) corresponds with 0.4 pg/µL. Note that a dual column system VOL. 37, NO. 5, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Concentrations of Individual POPs Determined in the Sample of Antarctic Weddell Seal (Leptonychotes Weddelli) Used for Method Validation compound
concentration (µg/kg wet weight)
R-HCH β-HCH Lindane Dieldrin Heptachlor, Aldrin p,p′-DDE p,p′-DDD p,p′-DDT sum DDT PCB 28 PCB 52/101 PCB 153 PCB 138 PCB 180 sum PCBs
0.8(0.1 not detecteda 0.7(0.2 4.6(0.5 not detecteda 8.8(1.0 1.9(0.2 3.4(0.4 14.1 0.4(0.1 not detectedb 1.1(0.1 0.5(0.1 0.4(0.1 2.0
compound
concentration (µg/kg wet weight)
B8-1413 3.6c B9-1679 2.4c B8--1412 1.5c B8-2229 0.4c B8-1414 0.4c B9-1025 0.9c sum Toxaphene 9.2 Oxychlordane 6.5c trans-Chlordane 0.6c cis-Chlordane 1.4c trans-Nonachlor 7.0c sum Chlordane 15.5 Q1 5.4c HCB qual. det.d
a Detection limit: 0.2 µg/kg. b Detection limit: 0.4 µg/kg. c n ) 1. Qualitatively detected at low concentrations, quantitative level not established due to coelution with an unknown compound. d
was used so that the real measured amount in the ECD represents just half of these values.
Results and Discussion Concentrations of POPs in the Blubber Sample Used for Method Validation. Highest concentrations of individual POPs were measured for p,p′-DDE, followed by transnonachlor, oxychlordane, dieldrin, and p,p′-DDT (Table 1). The natural heptachloro-1,2′-bipyrrole (23, 24) was prominent in the sample as well (5.4 µg/kg, one determination). Concentrations of chlordane- and DDT-related compounds were about 50% higher than those of CTTs (Table 1). On the other hand, contamination with PCBs played only a minor role which is in agreement with previous reports (25, 26). The good reproducibility (determined for PCB congeners, DDT-related compounds, and HCHs) confirmed that the present method including microwave-assisted extraction and gel-permeation chromatography is thus well suited to the determination of organochlorine compounds in marine mammals irrespective of the concentrations in the samples. Evaluation of Concentrations of POPs in Weddell Seals. Once the accuracy of the method was established, blubber
samples of three additional individuals were analyzed by using FOV-MAE. The range determined in the four individual samples was quite narrow (Table 2, study 1). It is known that organochlorine levels can vary significantly within a population. Despite the narrow range of concentrations determined in the four samples, we needed further evidence to show that these measurements are representative of the population of Weddell seals at King George Island as a whole. In a previous study, different Antarctic seal species from King George Island and from the Drescher Inlet were analyzed for toxaphene pollution (27). The PCB, DDT, and toxaphene (CTTs) burden in Antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina) from King George Island was comparable with the concentrations determined in the Weddell seals of the present study (27). Therefore, we conclude that POP concentrations determined in the Weddell seal samples are representive of the population at King George Island. Literature data of POP concentrations in Antarctic Weddell seals from other sampling places is also shown in Table 2. Other studies confirm the narrow range of POP concentrations in individuals at one site (at maximum factor 4) when carried out by the same analysts (Table 2, studies 2 & 3, 5 & 6, as well as 7 & 8). Factors that may cast doubt on the comparability of literature data are the use of different analytical techniques for sample cleanup and quantitation mode (GC/MS vs GC/ECD); the use of single congeners or technical PCB mixtures; and the referencing to lipid or wet weight. For this reason, we first compared the results with our own results from Weddell seals from Drescher Inlet (Table 2, studies 5 & 6). This comparison of samples analyzed with the same lab techniques show that PCB, DDT, chlordane, and CTT concentrations in Weddell seals from King George Island were more than 10-fold lower than those determined at Drescher Inlet. This result was also valid for the other populations of Weddell seals (Table 2). In this context it is worth discussing geographical variations of the sampling sites. Drescher Inlet and Neumayer Station in Weddell Sea, as well as Syowa in East Antarctica, are located between 72° and 69° S, while Jubany on King George Island is found at 62° S (Figure 1), i.e., above the southern polar circle. The distance to the south pole is ∼3,000 km at King George Island and still ∼2,000 km at Drescher Inlet in the Weddell Sea (Gould Bay in Weddell Sea provides the shortest distance from shore to the South Pole (1,234 km), and King George Island provides one of the longest, Table 2). King George Island (and further islands north of the Antarctic Peninsula) is the only landmass at 60-63° S (Figure 1). King George Island represents one of the greenest spots
TABLE 2. Concentrations of POPs (µg/kg wet weight) in the Blubber of Antarctic Weddell Seals Listed According to the Distance from South Pole study
n
1 2 3 4 5
4 ? 2 3 3 8 4 3 1 6 2
6 7 8 9 10
year of sampling
DDT
1993/4 1982 (?) 1981 1981 1990
11-19 150-186 97-1705 108 187-452
1-2.5 37-38 28-38e 310 10-40
1985 1995 1996 1966 (?) 1981
98-117 n.d. 17g 50h 80
74-85 406-750 395 n.d. 381
PCBs
distance to south pole (km)a
CTTs
location
geographic data
9-12b,c n.d.d n.d. n.d. 161-489b 154-622f n.d. n.d. n.d. n.d. n.d.
Jubany Syowa Syowa Atka Bay/Neumayer Drescher Inlet
62° 14′ S, 58° 40′ W 69° 00′ S, 39° 35′ E 69° 00′ S, 39° 35′ E 70° 39′ S, 08° 15′ W 72° 52′ S, 19° 25′ W
3090 2340 2340 2150 1910
Drescher Inlet Terra Nova Bay Terra Nova Bay McMurdo area Gould Bay
72° 52′ S, 19° 25′ W 74° 42′ S, 164° 7′ E 74° 45′ S, 164° 6′ E 77° 51′ S, 166° 40′ E ca. 77-78° S
1910 1700 1700 1350 1450-1340
reference this study (28) (25,29) (30) (27) (31) (26) (32) ( 7) (3) (30)
a Distances calculated from geographic data with the help of http://www.koordinaten.de/online/dist•bel.shtml. Values rounded to 10 km. Determined with GC/ECD. c n ) 3; sum of the individual compounds of technical toxaphene (CTTs) listed in Table 1. d Not determined. e Mean values of three samples of blubber; one newborn Weddell seal not used in Table. f Determined with GC/ECNI-MS (SIM mode). g Only p,p′-DDE. h Only identified in 4 of 16 samples. b
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PCB and DDT concentrations determined in the blubber of Weddell seals from King George Island are among the lowest ever determined in representative marine mammal samples. On the basis of the realistic premise that residues of POPs in marine mammals are a good indicator for the general pollution of a certain region, King George Island is one of the s if not the s least polluted marine regions in the world.
Acknowledgments We are grateful to the Institute of Organic Chemistry at the University of Jena and particularly the lab glass blowery for making the boron-silicate glass tubes and connection pieces available to us. We also are grateful to B. Luckas, head of the Department of Food Chemistry at the University of Jena, for providing general support. Thanks also to the colleagues at the Alfred Wegener Institute (Bremerhaven, Germany) for providing the samples collected at Drescher Inlet. W.V. acknowledges H.-U. Peter (Institute of Ecology, Jena, Germany) and the DAAD (Bonn, Germany) for making his travel to Antarctica possible.
Literature Cited
FIGURE 2. Average daily temperature cycles in (a) January (Antarctic summer) and (b) June (Antarctic winter) 1994 at Jubany, Syowa, McMurdo (some data points not available), and Neumayer stations (33). For geographic assignment see Figure 1. Mean temperatures at the south pole (Amundsen-Scott Station) on June 19, June 20, and January 24, 1994, were -51 °C, -45.1 °C, and -33 °C, respectively. in the Antarctic (11), and daily mean temperatures are significantly higher than those at Syowa (69° S), Neumayer (70° S), and McMurdo (77° S) stations (Figure 2). For instance, during the Antarctic summer 1994 (date of sampling of the Weddell seals), the daily mean temperatures at King George Island generally exceeded 0 °C. Note also that temperature cycles are mostly independent of each other (no common max. and min. temperatures). Moreover, temperatures at King George Island in June (winter) were comparable to January (summer) temperatures at the other sites (Figure 2). From this we conclude that the climate at 70° S is significantly harsher than that at 62° S (King George Island). The gradient in POP concentrations in Weddell seals suggests that deposition of POPs occurs south of King George Island. On the other hand, most locations at the same latitude as Drescher Inlet are found on the Antarctic continent (Figure 1). In the case of a regular atmospheric transport toward Antarctica it is possible that significant proportions of POPs are being deposited on the continent. Because of the lack of any surface water fluxes into the Southern Ocean (except the melting of ice during the Antarctic summer), only POPs that condense along the coast can reach living marine organisms as there are no higher terrestrial organisms in the Antarctic (the largest terrestrial species reaches 1.5 cm in size (11)). Clearly, the present study with Weddell seals does not allow us to prove this hypothesis about the food web, and systematic long-term measurements including air and snow samples from continental Antarctica are needed. However, our data clearly confirm geographical variations in the organochlorine concentrations in the Antarctic. Therefore, pollution time trends can be made only by comparing data from the same region, and correlations between different sites are difficult to make. Irrespective of these uncertainties,
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Received for review July 9, 2002. Revised manuscript received December 16, 2002. Accepted December 18, 2002. ES025949V
